How to export/import color palette from Brush in Texture Paint tab - Blender 2.8 Beta
If you save your palette in a blend file, you can append that palette into a new file to work with. name it something so you can differentiate it from generic names if you want to keep from losing track, but the steps are pretty straight forward.
File>Append, then navigate to the source blend file, and once appended, choose it from the palette drop down menu.